Coatings for building products and formulations for use with same

ABSTRACT

A formulation and dewaterable slurry for coating a building product. The coating formulation includes an hydraulic binder and a quantity of dewatering agent. A slurry is produced from said formulation and applied to the product to be coated. The resultant coating may be dewatered through said product. Dewatering can be accomplished with or without vacuum assistance.

PRIORITY CLAIM

[0001] This application claims priority from the following Australianprovisional patent applications, the full contents of which are herebyincorporated by cross-reference. Application No Title Date Filed PR3474A Composite Product 2 March 2001 PR3475 Spattering Apparatus 2 March2001 PR3476 Additive for a Dewaterable Slurry 2 March 2001 PR3477 AMethod and Apparatus for Forming a 2 March 2001 Laminated Sheet Materialby Spattering PR3478 Coatings for Building Products 2 March 2001

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to coatings and in particularcoatings for building products and laminated building products, andformulations for use with the same.

[0004] 2. Description of the Related Art

[0005] Any discussion of the prior art throughout the specificationshould in no way be considered as an admission that such prior art iswidely known or forms part of common general knowledge in the field.

[0006] There are a huge variety of mechanisms for applying coatings tobuilding products such as building boards.

[0007] The coatings can be divided into two main groups namely finishingcoatings, which are intended primarily for aesthetic purposes, andfunctional coatings which provide some additional structural or otherproperty/attribute to the resultant product.

[0008] The application technique depends to a large extent on theproperties of the coating composition and base layer or product to becoated. Manual application and spraying etc are most popular but theyrestrict the types of coating to be applied and indeed the buildingproduct to be coated. For example, when using a spray technique, onemust ensure the coating composition is of sufficient flowability to passthrough the spray nozzle but at the same time, the base material to becoated must be sufficiently rigid to withstand the impact of the spraycoating.

[0009] For certain building products, such as internal wall systems, asmooth surface finish is vital. Gypsum or plaster board is used almostexclusively as an internal wall board due to its excellent surfacefinish.

[0010] The use of fibre reinforced cement building board for instance asan internal wall board has significant advantages including cost andstructural integrity as compared with gypsum board. However, sometechniques for production of fibre reinforced cement sheets do notprovide a gypsum like surface finish. In response to public demand,builders require an internal wall board with a near perfect surfacefinish. Even minute irregularities which arise from production of fibrereinforced cement sheets can be sufficient to reject the product.Sanding the surface of the FRC sheet has been used to improve itssurface finish but in some instances such sanding can ‘feather’ or leaveexposed the reinforcing fibres thereby exacerbating the problem.

[0011] It is an object of the present invention to overcome orameliorate at least one of the disadvantages of the prior art, or toprovide a useful alternative.

SUMMARY OF THE INVENTION

[0012] In a first aspect, the present invention provides a method forcoating a building product comprising providing a coating formulationincluding a hydraulic binder and a quantity of dewatering agent,producing a slurry of said formulation, applying said slurry to theproduct to be coated and dewatering said slurry through said product.

[0013] In a second aspect, the present invention provides a formulationfor use in coating a building product comprising a hydraulic binder anda quantity of dewatering agent sufficient to permit dewatering of aslurry produced from said formulation through the building product.

[0014] In a third aspect, the present invention provides a dewaterableslurry for coating a building product, said slurry comprising water, ahydraulic binder and a quantity of dewatering agent sufficient to permitdewatering of said slurry through said building product.

[0015] In a fourth aspect, the present invention provides a compositeproduct comprising a base structural layer with a coating thereon, thecoating including a hydraulic binder and a quantity of dewatering agentsufficient such that the coating may be dewatered through the baselayer.

[0016] In a fifth aspect, the present invention provides a method ofmaking and improving a hydraulic binder based coating formulation forcoating a building product comprising adding to said binder a quantityof dewatering agent such that after application of a slurry of saidformulation to said building product, said slurry can be dewateredthrough the building product.

[0017] In a sixth aspect, the present invention provides a dewateringaid for dewatering a cementitious slurry coating on a product, saiddewatering aid comprising a quantity of particulate material sufficientto permit dewatering of the slurry through the product to be coated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Unless the context clearly requires otherwise, throughout thedescription and the claims, the words ‘comprise’, ‘comprising’, and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to”.

[0019] The dewatering agent serves to maintain sufficient porosity inthe slurry and product to be coated to permit dewatering of the slurrythrough the product to be coated. Preferably, the dewatering agent is aparticulate material such as fly ash, alumina trihydrate, silica flour,cenospheres (ceramic hollow spheres) or similar.

[0020] Fly ash is particularly preferred as it permits dewatering of theslurry within a few minutes. Other particulate dewatering agents such asalumina trihydrate or silica flour may also be used, however, theyincrease the time required for dewatering of the slurry through theproduct to be coated.

[0021] In a preferred embodiment, the slurry applied to the product tobe coated has a high water content. Preferably, the water content can beup to 50%. This is in contrast to previous cementitious formulationswhich generally have a higher solids content.

[0022] By combining the various components of the coating formulationdescribed above, a dewaterable slurry is obtained which can be appliedto the building product, dewatered through the building product andthereby provide a uniform coating over the building product.

[0023] Normally, after application of the coating, the resultant productwould be normally cured, steam cured or hydrothermally cured, ieautoclaved, and if required, sanded to a smooth flat finish.

[0024] The building product to which the coating can be applied isvirtually limitless provided the slurry can be dewatered through thebuilding product. Cementitious and gypsum building boards are typicalexamples of suitable building products on which the coating can beapplied.

[0025] The resultant coating, which may optionally contain fibres,results in a decorative finishing layer which is sandable, smooth, flat,low permeable, crack free and/or flexible, ready to be finished, forexample by painting.

[0026] The thickness of such a coating layer prior to sanding wouldrange from around 0.1 to 10 mm, preferably about 0.5 to 5 mm and mostpreferably about 1 to 3 mm.

[0027] After sanding, the finish layer may have a depth of around 0.05to 5 mm, preferably about 0.1 to 2 mm and most preferably about 0.5 to 1mm. The thus produced coated product is comparable in its workability tomonolithic (single layer) composites. It can be flexed, cut, drilled andfixed by nails etc to a frame without surface cracking or chipping.

[0028] The applicants have found an extremely good interlaminer bond andcompatibility between the dewatered slurry layer and base layerresulting in excellent composite action, compatibility and resistance todelamination.

[0029] The term ‘hydraulic binder’ as used throughout the specificationrefers to a pulverised material in the solid, dry state which, whenmixed with water, yields plastic mixtures that are able to set andharden, for example a cement. Included within the definition are white,grey or pigmented cements and hydraulic limes.

[0030] The term ‘cement’ includes hydraulic and alite cements such asportland cement, blended cements such as portland cement blended withfly ash, blast-furnace slag, pozzalans and the like and mixturesthereof, masonry cement, oil well cement, natural cement, aluminacement, expansive cements and the like, or mixtures thereof.

[0031] The quantity of binder in the formulation is preferably betweenabout 10 to 50 wt % based on the total dry ingredients, more preferablyabout 15 to 40 wt % and most preferably about 20 to 30 wt %.

[0032] The fly ash used in the present invention provides a number ofadvantages including, particularly, as an aid to dewatering of theslurry as defined above.

[0033] The term ‘fly ash’ as used herein refers to a solid powder havinga chemical composition similar to or the same as the composition ofmaterial that is produced during combustion of powdered coal, ie about25 to 60 wt % silica, about 10 to 30 wt % Al₂O₃, about 5 to 25 wt %Fe₂O₃, about 0 to 20 wt % CaO and about 0 to 5 wt % MgO.

[0034] Fly ash particles are typically spherical and range in diameterfrom about 1 to 100 microns. In a preferred embodiment, the fly ashcomprises two components. A first ‘larger’ size particles of fly ashwith preferably about a 100 micron maximum size. This size range of flyash is used in the slurry to aid in improving the dewateringcharacteristics of the slurry but also as a moderately reactivepozzalan.

[0035] The second ‘smaller’ fly ash size zone which preferably has abouta 10 micron maximum size also adds an improving dewateringcharacteristic but is a more highly reactive pozzalan. This ‘smaller’fly ash particle zone also improves the sanded surface quality of thefinish layer.

[0036] In a preferred embodiment, the first fly ash comprises about 10to 60 wt % of the formulation based on total dry ingredients, morepreferably about 20 to 50 wt % and most preferably about 30 to 40 wt %.

[0037] The second fly ash component preferably provides about 5 to 30 wt% of the formulation based on total dry ingredients, more preferablyabout 10 to 25 wt % and most preferably about 15 to 20%.

[0038] In another preferred embodiment, the dewatering agent may includea coarse fraction fly ash which is greater than about 100 microns. Thiscoarse fraction fly ash includes bottom ash or similar products fromcoal combustion. There is an advantage to using these products over theaforementioned particle size fly ash since it is cheaper. Of course, aswill be clear to persons skilled in the art, some reformulation of theslurry may be required to provide a suitable coating and appropriatedewatering characteristics when the dewatering agent is such a coarsefraction fly ash.

[0039] The coating may optionally contain other additives such asfillers. Such fillers may also be used to improve the dewateringcharacteristics of the slurry. For example, cenospheres (hollow ceramicmicrospheres) diatomite, wollastonite, ground rice hulls, ground perliteor the like, are particularly suitable for this purpose.

[0040] These and other fillers may also be used to provide additionalbenefits, for example calcium carbonates or alumina hydrates improvesandability and flexibility of the coated layer respectively. Silicaflour improves hardness of the sanded surface of the coating layer andthe acoustic/thermal insulation properties of the layer can be improvedby including rubber particles, vermiculite, perlite, expandedpolystyrene or gypsum.

[0041] The fillers preferably comprise about 5 to 30 wt % of theformulation based on total dry ingredients, more preferably about 10 to25 wt % and most preferably about 25 to 20 wt %.

[0042] The coating may also contain other organic additives. Cementplasticising agents, for example, may be used to alter the rheology ofthe slurry. Suitable cement plasticising agents include melaminesulphonate formaldehyde condensates, naphthalene sulphonate formaldehydecondensates, naphthalene sulphonates, calcium lignosulphonates, sodiumlignosulphonates, saccharose, sodium gluconate, sulphonic acids,carbohydrates, amino carboxylic acids, polyhydroxycarboxilic acids,sulphonated melomine and the like.

[0043] The amount of cement plasticiser of course will depend upon thefluidising ability of the particular plasticisers. Generally thequantity of plasticiser will be in the range of about 0.3 to 3 wt % andmore preferably about 0.5 to 2 wt % based on the total of dryingredients in the formulation.

[0044] Particularly preferred cement plasticisers are Melment F-10, amelamine formaldehyde sodium bisulphate polymer dispersant marketed bySKW-Trostburg in the form of a fine white powder. Another suitableplasticiser is Neosyn, a condensed sodium salt of sulphonatednaphthalene formaldehyde available from Hodgson Chemicals.

[0045] Another preferred component in the coating is a biopolymer whichacts to enhance the flowability, segregation resistance and selflevelling qualities of the cementitious slurry. Particularly suitablebioplymers are xanathan gum and/or whelan gum, eg KELCO-CRETE, K1C 376manufactured by Monsanto.

[0046] Latex may also be included in the coating composition to improveadherence, elasticity, stability and impermeability of the coating. Thelatex also improves flexibility of the formed coating.

[0047] The latex may be selected from the group consisting of acryliclatex, styrene latex, butadiene latex or mixtures thereof and isprovided preferably in an amount between about 0.5 to 20%, morepreferably about 1 to 15% and most preferably about 10% by weight ofcement (on polymer solids basis) solids.

[0048] Vinyl polymers may also be incorporated into the coating eitherin addition or as a substitute to the latex emulsions. Such vinylpolymers or equivalent polymeric materials enhance adhesion, resilienceand flexural strength and abrasion resistance of the coating.

[0049] Preferred vinyl polymers include polyvinyl acetate or a copolymervinyl acetate with another monomer such as ethylene. A particularlypreferred vinyl acetate resin is VINNAPAS LL5044 thermo plastic resinpowder which contains a vinyl acetate-ethylene copolymer available fromWacker. Such powdered vinyl polymer is preferably provided in quantitiessimilar to the latex emulsion referred to above.

[0050] In addition to the above, conventional other additives such asmineral oxides, hydroxides and clays, metal oxides and hydroxides, fireretardants such as magnesite, thickeners, silica fume or amorphoussilica, water sealing agents, water reducing agents, setting modifiers,hardeners, dispersants, foaming agents or flocculating agents,water-proofing agents and density modifiers are suitable for use withthe present invention.

[0051] In this regard, one particular advantage arising from the presentinvention is the ability to treat the product to be coated by providingadditives in the coating. To explain, since the coating is dewateredthrough the product to be coated, it is possible to provide additives tothe base layer by incorporation in the slurry. For instance, awaterproofing agent such as silane may be included in the coating inexcess of the coating layers requirements. During dewatering, the silanewill be drawn into and through the base layer being coated therebytreating the base layer. This simultaneous treatment of the base layeras well as coating the base layer is a valuable additional benefitarising from the aforedescribed method.

EXAMPLES

[0052] The preferred embodiments of the present invention will now bedescribed by way of example only with reference to the followingembodiments.

[0053] In each of the following examples, the product was produced asfollows.

[0054] Step 1 Slurry Preparation

[0055] A slurry of the formulation is prepared by mixing the hydraulicbinder, fly ash and other optional components with water. The solidscontent in the slurry is preferably between about 50 and 90%, morepreferably about 55 to 80% and most preferably about 60 to 70%.

[0056] Step 2 Slurry Application/Dewatering

[0057] The slurry is applied to the base layer by any convenient meanssuch as brushes rollers, knives or sprays etc. In a particularembodiment the slurry is applied by means of the apparatus and methodsubject of Australian Provisional Patent Application Nos. PR3475 andPR3477, which are incorporated herein by reference.

[0058] The slurry is preferably designed to self level and form auniform coating on the product. The building product to be coatedexhibits s certain degree of porosity causing the slurry to dewater andform a uniform deposited cementitious layer. Time for dewatering canvary quite dramatically but normally occurs between about 10 and 90seconds, depending on the porosity of the material to be coated, itswater content and thickness and viscosity of the slurry formulation. Avacuum may be used to reduce the slurry dewatering time if required.This is particularly useful when tailoring the coating process to thespeed of a building product forming process, eg between about 40 to 45seconds on a Hatschek production line.

[0059] Step 3 Curing

[0060] After forming, the green laminate article comprising the buildingproduct plus coating is preferably precured for a short time, eg up toabout 48 hours, then cured by air/moist curing at room temperature,steam curing between about 40 and 90° C. or autoclaving in a steampressure vessel between about 120 and 200° C.

[0061] For either of these three curing techniques, a curing time rangebetween about 6 and 72 hours, preferably up to about 48 hours, issuitable. Of course, as will be clear to persons skilled in the art, thelength of time chosen for curing is dependent on the formulation, themanufacturing process and form of the article.

[0062] The following examples relate to specific formulationcompositions.

Example 1 Sandable Dewatered Slurry Composition

[0063] Function:

[0064] sandable, durable finishing layer for facade applications.

[0065] The low viscosity slurry (drainage time in 50 ml volumefunnel=3.4 seconds) was applied on the base layer (Hardiform™ 12 mmthick cellulose fibre reinforced cement-based green sheet manufacturedby James Hardie Industries). The slurry dewatered in 90 seconds(un-aided by vacuum) forming a 1.25 mm thick coating. The coated sheetwas autoclave-cured for 8 hrs at 180° C. temperature and 0.80 MPapressure. It was then sanded flat to 0.60 mm thick using industrialsanders equipped with 100 grit sand paper belts. % by total Slurryweight of Composition solids (S) Weight in gm Dewatered CementitiousComposition Portland Cement 30 12000 Silica Flour (400 G 10 4000 grade)Fly ash (larger size 40 16000 fraction) Fly ash (smaller size 20 8000fraction) Total 100 40000 Water (W) 14000 Water/Solids (W/S 0.35 ratio)Solids Content 0.74 (W/W + S) Organic Additives Welan Gum 0.0075 3.0(Kelcocrete) naphthalene 0.25 100.0 formaldehyde Plasticising Agent(Neosyn) Acrylic Emulsion 1.0 400.0 Rhoplex MC 1934

Example 2 Rubberised Dewatered Slurry Composition

[0066] Function:

[0067] Finishing layer in skid-resistant flooring, hard wearing staticdissipative flooring and acoustic insulating ceiling panels.

[0068] The low viscosity slurry (drainage time in 50 ml volumefunnel=4.2 seconds) was applied on the base layer (Hardiform™ 12 mmthick cellulose fibre reinforced cement-based green sheet manufacturedby James Hardie Industries). The slurry dewatered in 60 seconds(un-aided by vacuum) forming a 1.25 mm thick coating. The coated sheetwas autoclave-cured for 8 hrs at 180° C. temperature and 0.80 MPapressure. It was then sanded flat to 0.60 mm thick using industrialsanders equipped with 100 grit sand paper belts. % by total Slurryweight of Composition solids (S) Weight in gm Dewatered CementitiousComposition Portland Cement 30 12000 Recycled Rubber crumbs 10 4000(minus 30 mesh) Fly ash(larger size 40 16000 fraction) Fly ash(smallersize 20 8000 fraction) Total 100 40000 Water 13000 Water/Solids (W/S0.325 ratio) Solids Content 0.755 (W/W + S) Organic Additives Welan Gum(Kelcocrete) 0.0075 3.0 naphthalene 0.25 100.0 formaldehyde PlasticisingAgent (Neosyn) Acrylic Emulsion 1.0 400.0 Rhoplex MC1934

Example 3 Flexible & Sandable Dewatered Slurry Composition

[0069] Function:

[0070] Flexible & sandable finishing layer on thin fibre cementreinforced cement-based lining.

[0071] The low viscosity slurry (drainage time in 50 ml volumefunnel=2.8 seconds) was applied on the base layer (Hardiflex™ 4.5 mmthick cellulose fibre reinforced cement-based green sheet manufacturedby James Hardie Industries). The slurry dewatered in 120 seconds(un-aided by vacuum) forming a 1.25 mm thick coating. The coated sheetwas precured for 48 hours then was autoclave-cured for 8 hrs at 180° C.temperature and 0.80 MPa pressure. It was then sanded flat to 0.60 mmthick using industrial sanders equipped with 100 grit sand paper belts.% by total Slurry weight of Composition solids (S) Weight in gmDewatered Cementitious Composition Portland Cement 20 8000 CalciumCarbonate 10 4000 Grade 10 (40 um avg. size) Alumina Tri-hydrate 5 2000(80 um avg. size) Fly ash (larger size 45 18000 fraction) Fly ash(smaller size 20 8000 fraction) Total 100 40000 Water 12000 Water/Solids (W/S 0.30 ratio) Solids Content 0.77 (W/W + S) Organic AdditiveWelan Gum (Kelcocrete) 0.0075 3.0 naphthalene 0.25 100.0 formaldehydePlasticising Agent (Neosyn) Styrene Acrylic Latex 5 2000 Emulsion (56%solids)

Example 4 Flexible & Sandable Dewatered Slurry Composition (Low Cement)

[0072] Function:

[0073] Flexible & sandable finishing layer on thin fibre cementreinforced cement-based lining.

[0074] The low viscosity slurry (drainage time in 50 ml volumefunnel=4.5 seconds) was applied on the base layer (Hardiflex™ 4.5 mmthick cellulose fibre reinforced cement-based green sheet manufacturedby James Hardie Industries). The slurry dewatered in 90 seconds(un-aided by vacuum) forming a 1.25 mm thick coating. The coated sheetwas autoclave-cured for 8 hrs at 180° C. temperature and 0.80 MPapressure. It was then sanded flat to 0.60 mm thick using industrialsanders equipped with 100 grit sand paper belts. % by total Slurryweight of Composition solids (S) Weight in gm Dewatered CementitiousComposition Portland Cement 10 4000 Calcium Carbonate 20 8000 Grade 10(40 um avg. size) Alumina Tri-hydrate 5 2000 (80 um avg. size) Fly ash(larger size 40 18000 fraction) Fly ash (smaller size 25 10000 fraction)Total 100 40000 Water 16000 Water/Solids (W/S 0.40 ratio) Solids Content0.715 (W/W + S) Organic Additives Welan Gum (Kelcocrete) 0.0075 3.0naphthalene 0.25 100.0 formaldehyde Plasticising Agent (Neosyn) Vinylacetate-ethylene 1.625 650 powdered copolymer (Vinnapas LL5004)

[0075] The aforementioned examples provide a coated product comparablein workability to monolithic or single layer composites. They can beflexed, cut, drilled or fixed by nails or the like to a frame withoutsurface cracking or chipping.

[0076] The surface is ‘finish-ready’ and remains smooth, flat,crack-free and with low permeability even when used in a curvedconfiguration.

[0077] Each examples provided excellent interlaminer bond between thebase sheet and coating exhibiting good composite action, compatibilityand resistance to delamination.

[0078] It can be seen that the present process provides a significantimprovement not only in the attributes of the product but also in theability to tailor the surface finish of a building product to matchparticular requirements. Examples of particular formulations to providethe desired finish characteristic include

[0079] a) Terrazzo (hardwearing decorative finish)—the finishing layerof the dewatered slurry can contain marble chips and pigmented cementsand fillers. It may then be sanded and polished to form a hardwearingdecorative finish. Such a coating on, for example, a fibre cementbacking board, could be used as flooring tiles, decorative wall liningor external prefinished fibre cement cladding.

[0080] b) Stucco (orange peel) Finish—this may be achieved bymanipulating speed and volume of the applied slurry to achieve a stuccolook on the finishing layer. Once again, such a product may be used asan external pre-finished cement cladding.

[0081] c) Sandable finish—this is probably the simplest and moststraightforward application of the coating technique to provide acoating layer which may be sanded and sealed, thereby providing a paintready smooth, crack-free and low permeable surface. Such a product maybe used for a variety of internal and external uses.

[0082] d) Flexible finish—the coating layer may include various fillersand other additives to improve its flexibility, eg ethylene vinylacetate, styrene butadiene rubber, styrene acrylic. It is designed to bea sandable, workable ie by score and snap, nailable, crack-free,non-chipping, flexible and bendable, paint ready surface. Such a coatingcould normally be applied to reasonably thin building product to permitflexibility. It has a wide variety of uses but is particularly suitableas an internal lining in wet area applications or as an externalcladding element, eg as a paint ready fibre cement siding.

[0083] e) Skim-coated finish—such a coating of the dewatered slurry maybe applied to gypsum based building products thereby providing a smooth,flat, pre-skim coated and paint ready surface.

[0084] f) Rubberised finish—by the addition of rubber crumbs into theslurry formulation, a coating layer may be provided on say a fibrecement backing for use as a skid resistant flooring, hardwearing staticdissipative flooring or acoustic insulating ceiling panels.

[0085] It will be understood by persons skilled in the art that thepresent invention may be embodied in other forms without departing formthe spirit or scope of the inventive idea as described herein. Inparticular, it will be appreciated that the formulations, coatings,additives, methods and composite products of the present invention aresuitable or may be adapted for use in conjunction with the methods andapparatus as described in the various priority documents.

What is claimed is:
 1. A formulation for use in coating a buildingproduct comprising: a hydraulic binder; and a quantity of dewateringagent sufficient to permit dewatering of a slurry produced from saidformulation through the building product.
 2. A formulation according toclaim 1, wherein the dewatering agent is provided in a sufficientquantity to maintain porosity in the slurry and the product to be coatedduring dewatering.
 3. A formulation according to claim 1, wherein thedewatering agent is a particulate material.
 4. A formulation accordingto claim 1, wherein the dewatering agent is selected from fly ash,alumina trihydrate, silica flour, cenospheres or mixtures thereof.
 5. Aformulation according to claim 1, wherein the coating includes fibres.6. A formulation according to claim 1, wherein the hydraulic binder usedin the coating is selected from the group consisting of white, grey orpigmented cements, hydraulic limes and mixtures thereof.
 7. Aformulation according to claim 1, wherein the hydraulic binder used inthe coating is selected from the group consisting of Portland cement,blended cements, blast furnace slag, pozzalans, masonry cement, oil wellcement, natural cement, alumina cement, expansive cements and mixturesthereof.
 8. A formulation according to claim 1, wherein the binder inthe formulation is between about 10 and 50 wt % based on total dryingredients.
 9. A formulation according to claim 1, wherein fly ash isthe dewatering agent.
 10. A formulation according to claim 9, whereinthe dewatering agent comprises: i) about 10 to 60% of the formulationbased on total dry ingredients of a first fly ash component having aparticle diameter between about 1 and 100 microns; and ii) about 5 to 30wt % of the formulation based on total dry ingredients of a second flyash component having a maximum particle size diameter of around 10microns.
 11. A formulation according to claim 1, wherein the dewateringagent includes a coarse fraction fly ash having a particle size diametergreater than about 100 microns.
 12. A formulation according to claim 1,wherein the formulation includes additives to improve resultantproperties of the coating.
 13. A formulation according to claim 1,wherein the formulation includes additives to improve workability andapplicability of the slurry to the product to be coated.
 14. Aformulation according to claim 1, wherein the formulation includesadditives to improve the properties of the building product to be coatedsuch that upon dewatering of the coating through the product, thebuilding product is thus treated with said additive.
 15. A dewaterableslurry for coating a building product, said slurry comprising water, ahydraulic binder and a quantity of dewatering agent sufficient to permitdewatering of said slurry through said building product.
 16. Adewaterable slurry according to claim 15, wherein the dewatering agentis provided in a sufficient quantity to maintain porosity in the slurryand the product to be coated during dewatering.
 17. A dewaterable slurryaccording to claim 15, wherein the dewatering agent is a particulatematerial.
 18. A dewaterable slurry according to claim 15, wherein thedewatering agent is selected from the group consisting of fly ash,alumina trihydrate, silica flour, cenospheres and mixtures thereof. 19.A dewaterable slurry according to claim 15, wherein the slurry has awater content of up to about 50%.
 20. A dewaterable slurry according toclaim 15, wherein the coating includes fibres.
 21. A dewaterable slurryaccording to claim 15, wherein the hydraulic binder used in the coatingis selected from the group consisting of white, grey or pigmentedcements, hydraulic limes and mixtures thereof.
 22. A dewaterable slurryaccording to claim 15, wherein the hydraulic binder used in the coatingis selected from the group consisting of Portland cement, blendedcements, blast furnace slag, pozzalans, masonry cement, oil well cement,natural cement, alumina cement, expansive cements and mixtures thereof.23. A dewaterable slurry according to claim 15, wherein the binder inthe formulation is between about 10 and 50 wt % based on total dryingredients.
 24. A dewaterable slurry according to claim 15, wherein flyash is the dewatering agent.
 25. A dewaterable slurry according to claim24, wherein the dewatering agent comprises: i) about 10 to 60% of theformulation based on total dry ingredients of a first fly ash componenthaving a particle diameter between about 1 and 100 microns; and ii)about 5 to 30 wt % of the formulation based on total dry ingredients ofa second fly ash component having a maximum particle size diameter ofaround 10 microns.
 26. A dewaterable slurry according to claim 15,wherein the dewatering agent includes a coarse fraction fly ash having aparticle size diameter greater than about 100 microns.
 27. A dewaterableslurry according to claim 15, wherein the formulation includes additivesto improve resultant properties of the coating.
 28. A dewaterable slurryaccording to claim 15, wherein the formulation includes additives toimprove workability and applicability of the slurry to the product to becoated.
 29. A dewaterable slurry according to claim 15, wherein theformulation includes additives to improve the properties of the buildingproduct to be coated such that upon dewatering of the coating throughthe product, the building product is thus treated with said additive.30. A detwaterable slurry according to claim 15, wherein the slurry isself levelling.
 31. A dewaterable slurry according to claim 15, whereinthe resultant dewatered slurry is curable by air curing, steam curing orhydrothermal curing in an autoclave.
 32. A detwaterable slurry accordingto claim 15, wherein the slurry may be applied to the product to becoated by splattering.